Many of the processes utilized in various industries, such as those used in the chemical, pharmaceutical and food industries, use valves to control fluid flow. It is desirable to monitor the operational state of a valve, such as whether the valve is opened or closed, to ensure that a particular process or activity is actually being performed. One method for monitoring the operational state of a valve is through the use of a position sensor.
One type of position sensor utilizes a proximity switch to detect whether a valve is opened or closed. The proximity switch utilizes ferromagnetic reed elements having contacts which are activated in the presence of a magnetic field. The proximity switch may be configured such that the contacts are normally open and then close in the presence of a magnetic field so as to complete an electric circuit. Alternatively, the proximity switch is configured such that the contacts are normally closed and are then opened in the presence of a magnetic field. The magnetic field may be provided by a magnet located in a target element.
Referring to FIG. 1, a configuration for monitoring the operational state of a valve utilizing first 10 and second 12 proximity switches is shown. The first 10 and second 12 proximity switches are mounted on a first bracket 14 attached to a portion of a valve 16. First 18 and second 20 target elements are mounted to a second bracket 22 and are spaced apart from the first 10 and second 12 proximity switches. The first 18 and second 20 target elements each include a magnet for actuating the first 10 and second 12 proximity switches, respectively. The second bracket 22 is attached to a moveable portion of the valve 16 such as a knife gate portion of a knife gate valve. The second bracket 22 and the first 18 and second 20 target elements move as shown by the arrows 21 as the knife gate travels between open and closed positions. In FIG. 1, the first target element 18 is shown positioned adjacent to the first proximity switch 10. In this position, a magnetic field of the first target element 18 activates the first proximity switch 10 to thus indicate a first operational state for the valve 16. In use, the knife gate and thus the second bracket 22 move to a position wherein the knife gate valve is either opened or closed. When this occurs, the second target element 20 is positioned adjacent to the second proximity switch 12. In this position, a magnetic field of the second target element 20 activates the second proximity switch 12 to thus indicate a second operational state for the valve 16.
Proximity switches are electrically connected to a control monitor that monitors whether the switch is activated or deactivated. It would be desirable for proximity switches to also provide a visual indication of whether the switch is activated or deactivated.